1. Technical Field
The present invention generally relates to a method of producing a liquid ejecting head unit that has a plurality of liquid ejecting heads combined with one another. Each of the plurality of liquid ejecting heads to which the invention is directed is provided with a fluid channel formation substrate, which has pressure generation chambers that are in communication with nozzle orifices through which liquid is ejected, and piezoelectric elements, each of which is made up of a lower electrode, a piezoelectric layer, and an upper electrode, formed on one surface of the fluid channel formation substrate. More particularly, the invention relates to a method of producing an ink-jet recording head unit that has a plurality of ink-jet recording heads combined with one another, where the ink-jet recording heads discharge ink as an example of a variety of liquid.
2. Related Art
As a known configuration of an ink-jet recording head unit (hereafter referred to as a head unit) that is provided with a plurality of ink-jet recording heads, a head unit of related art is provided with a plurality of ink-jet recording heads that discharge ink supplied from ink cartridges or the like through nozzle orifices, head cases that are bonded to one surface of the ink-jet recording heads that is opposite to the ink-discharging surface thereof, and a cartridge case which supports the plurality of the ink-jet recording heads and the head cases. A typical example of such a known configuration is described in JP-A-2001-162811 (specifically, refer to FIG. 2 thereof).
A typical ink-jet recording head is provided with a fluid channel formation substrate, which has pressure generation chambers that are in communication with nozzle orifices from which ink is discharged. Such a typical ink-jet recording head is further provided with piezoelectric elements that are made up of a lower electrode, a piezoelectric layer, and an upper electrode, where the piezoelectric elements are formed on one surface of the fluid channel formation substrate with a vibrating plate being interposed therebetween. When a voltage is applied between the upper electrode and the lower electrode of the piezoelectric element, the piezoelectric layer gets deformed. As the piezoelectric layer becomes deflected, a pressure change occurs inside the pressure generation chamber; and as a result thereof, ink is discharged from the nozzle orifice.
It is known in the art that the piezoelectric layer of the piezoelectric element used in such an ink-jet recording head is made of dielectric material, and has hysteresis characteristic in a polarization electric field.
A related art disclosed in JP-A-2003-243741 (specifically, refer to Pages 5 and 7 as well as FIGS. 1 and 6 thereof) proposes the application of a voltage to a piezoelectric layer having two coercive electric fields located in the same electric-field polarity, where the voltage provides an electric-field intensity that is not less than the coercive electric fields.
However, the coercive electric fields of the piezoelectric layers vary from one to another. Therefore, if an ink-jet recording head unit is produced from a combination of a plurality of ink-jet recording heads that have piezoelectric layers whose coercive electric fields vary significantly from one to another, it is impossible to equalize the displacement characteristic of the piezoelectric elements of one ink-jet recording head with that of other ink-jet recording heads when the plurality of ink-jet recording heads are driven by a driving pulse having the same waveform. As a result thereof, disadvantageously, it is impossible to uniformize (i.e., make uniform) the ink-discharge characteristic of the plurality of the ink-jet recording heads assembled into one head unit.
On the other hand, a more complex configuration will be required if pulses having waveforms different from one another are used to drive the plurality of ink-jet recording heads of one head unit that have coercive electric fields varying from one to another, which results in increased production cost.
The same problem occurs if two coercive electric fields of the piezoelectric layer in hysteresis characteristic are located in the same electric-field polarity as disclosed in JP-A-2003-243741.
The above-identified problem is not unique to a method of producing an ink-jet recording head unit that has a plurality of ink-jet recording heads combined with one another. That is, the above-identified problem could also occur in a method of producing a variety of liquid ejecting head unit that has a plurality of liquid ejecting heads combined with one another, where the plurality of liquid ejecting heads eject various kinds of liquid including ink but not limited thereto.